mosaic2

Francisco Valdes wrote on Dec 05, 2005

From: "Liliana Hernandez Martinez" <lhernand@astroscu.unam.mx ([email]lhernand@astroscu.unam.mx[/email])>
Date: November 8, 2005 7:58:18 AM MST
To: Frank Valdes <valdes@noao.edu ([email]valdes@noao.edu[/email])>
Subject: Re: mosaic2

Thank you for your answer, actually I can pass the cosmic rays and bad pixel mask process, bur now 
I am traying to combine or stack my images in order to get a more deep image. So I am fighting with 
the WCS, I am running the mscimatch for the tangent-plane projected images. In your notes you say 
that:

 "If the data were taken under photometric conditions the relative scales should all be very very close 
to 1. If there is a severe outlier, investigate that image. It may have a WCS that is not accurate 
enough and you might have to rerun msccmatch on the pretangent-plane projected image."

I have rerun the msccmatch on the pretangent-plane projected image, and projected again, and what 
I get is:

MSCIMATCH:
  Reading region coordinates from mos081as.usnoA2
    3000 coordinates read
  Measuring regions in mos081as.fits ...
  Using bad pixel mask mos081a_bpm ...
    1550 good regions measured
  Measuring regions in mos082as.fits ...
  Using bad pixel mask mos082a_bpm ...
    1530 good regions measured
  Measuring regions in mos083as.fits ...
  Using bad pixel mask mos083a_bpm ...
    1527 good regions measured
  Measuring regions in mos084as.fits ...
  Using bad pixel mask mos084a_bpm ...
    1520 good regions measured
  Determining scale factors ...
       mos081as.fits: 1.0000 (0.0000)     0.00 (0.00)
       mos082as.fits: 0.2439 (0.0012)   468.06 (0.00)
       mos083as.fits: 0.1034 (0.0005)  1314.19 (0.00)
       mos084as.fits: 0.1011 (0.0006)  1346.87 (0.00)
Accept scaling and update images? (yes): 

In your experience, can I accept this scaling? or there is something else that I can do?

Unfortunatelly, our observations aren't under photometric conditions, we had some clouds. Our data 
are dithered in the configuration (0,0) and (160, -240).

thank you very much.

sincerely

Liliana.

@===@===@===@===@===@===@===@===@
L.
Instituto de Astronomía en Ciudad Universitaria, D.F.
Apartado Postal 70-264   México, 04510 D.F. 
Tel. 56 22 39 30  
Fax. 56 16 06 53

From: Frank Valdes <valdes@noao.edu ([email]valdes@noao.edu[/email])>
Date: November 14, 2005 1:55:55 PM MST
To: Liliana Hernandez Martinez <lhernand@astroscu.unam.mx ([email]lhernand@astroscu.unam.mx[/email])>
Subject: Re: mosaic2

Hi Liliana,

The scale factors you report for mscimatch (matching of the intensities) are possibly correct though I could not say for sure without looking at the images.  It should be easy to quickly check if the numbers are approximately right.  You would use something like IMEXAM  and the 'a' key to do rough photometry of stars which you identify visually as being the same star.  The ratio of the flux between one image and mos081as.fits should be close to the value shown in the mscimatch output.  In other words you would check the ratio of photometry between two images which is what the scale factors mean.  If you get something around 1 and mscimatch shows 0.2 then there is probably something wrong with the matching of stars for the photometry, which would be caused by the WCS not being correct.

If mscimatch is not working right for you, you could just measure the relative intensities of the different frames using IMEXAM or other photometry tool and then set the relative scale values in the header or in a file for use with mscstack.   You can read the help for mscstack to find out how the relative scales can be specified.

Yours,
Frank

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Last post on Dec 05, 2005